Commit | Line | Data |
---|---|---|
79c94bd3 JA |
1 | /* |
2 | This is a maximally equidistributed combined Tausworthe generator | |
3 | based on code from GNU Scientific Library 1.5 (30 Jun 2004) | |
4 | ||
5 | x_n = (s1_n ^ s2_n ^ s3_n) | |
6 | ||
7 | s1_{n+1} = (((s1_n & 4294967294) <<12) ^ (((s1_n <<13) ^ s1_n) >>19)) | |
8 | s2_{n+1} = (((s2_n & 4294967288) << 4) ^ (((s2_n << 2) ^ s2_n) >>25)) | |
9 | s3_{n+1} = (((s3_n & 4294967280) <<17) ^ (((s3_n << 3) ^ s3_n) >>11)) | |
10 | ||
11 | The period of this generator is about 2^88. | |
12 | ||
13 | From: P. L'Ecuyer, "Maximally Equidistributed Combined Tausworthe | |
14 | Generators", Mathematics of Computation, 65, 213 (1996), 203--213. | |
15 | ||
16 | This is available on the net from L'Ecuyer's home page, | |
17 | ||
18 | http://www.iro.umontreal.ca/~lecuyer/myftp/papers/tausme.ps | |
19 | ftp://ftp.iro.umontreal.ca/pub/simulation/lecuyer/papers/tausme.ps | |
20 | ||
21 | There is an erratum in the paper "Tables of Maximally | |
22 | Equidistributed Combined LFSR Generators", Mathematics of | |
23 | Computation, 68, 225 (1999), 261--269: | |
24 | http://www.iro.umontreal.ca/~lecuyer/myftp/papers/tausme2.ps | |
25 | ||
26 | ... the k_j most significant bits of z_j must be non- | |
27 | zero, for each j. (Note: this restriction also applies to the | |
28 | computer code given in [4], but was mistakenly not mentioned in | |
29 | that paper.) | |
30 | ||
31 | This affects the seeding procedure by imposing the requirement | |
32 | s1 > 1, s2 > 7, s3 > 15. | |
33 | ||
34 | */ | |
35 | ||
1fbbf72e | 36 | #include "rand.h" |
637ef8d9 | 37 | #include "../hash.h" |
1fbbf72e | 38 | |
1fbbf72e JA |
39 | static inline int __seed(unsigned int x, unsigned int m) |
40 | { | |
41 | return (x < m) ? x + m : x; | |
42 | } | |
43 | ||
2615cc4b JA |
44 | static void __init_rand(struct frand_state *state, unsigned int seed) |
45 | { | |
46 | int cranks = 6; | |
47 | ||
48 | #define LCG(x, seed) ((x) * 69069 ^ (seed)) | |
49 | ||
50 | state->s1 = __seed(LCG((2^31) + (2^17) + (2^7), seed), 1); | |
51 | state->s2 = __seed(LCG(state->s1, seed), 7); | |
52 | state->s3 = __seed(LCG(state->s2, seed), 15); | |
53 | ||
54 | while (cranks--) | |
55 | __rand(state); | |
56 | } | |
57 | ||
1fbbf72e JA |
58 | void init_rand(struct frand_state *state) |
59 | { | |
2615cc4b JA |
60 | __init_rand(state, 1); |
61 | } | |
62 | ||
63 | void init_rand_seed(struct frand_state *state, unsigned int seed) | |
64 | { | |
65 | __init_rand(state, seed); | |
1fbbf72e | 66 | } |
637ef8d9 | 67 | |
7d9fb455 | 68 | void __fill_random_buf(void *buf, unsigned int len, unsigned long seed) |
637ef8d9 | 69 | { |
637ef8d9 JA |
70 | long *ptr = buf; |
71 | ||
637ef8d9 | 72 | while ((void *) ptr - buf < len) { |
7d9fb455 | 73 | *ptr = seed; |
637ef8d9 | 74 | ptr++; |
7d9fb455 JA |
75 | seed *= GOLDEN_RATIO_PRIME; |
76 | seed >>= 3; | |
637ef8d9 JA |
77 | } |
78 | } | |
7d9fb455 | 79 | |
3545a109 JA |
80 | unsigned long fill_random_buf(struct frand_state *fs, void *buf, |
81 | unsigned int len) | |
7d9fb455 | 82 | { |
3545a109 | 83 | unsigned long r = __rand(fs); |
7d9fb455 JA |
84 | |
85 | if (sizeof(int) != sizeof(long *)) | |
3545a109 | 86 | r *= (unsigned long) __rand(fs); |
7d9fb455 JA |
87 | |
88 | __fill_random_buf(buf, len, r); | |
89 | return r; | |
90 | } |